The Datomic Architecture and Data Model

Reference: The Datomic Architecture and Data Model

Rich Hickey:

This is not a schemaless system. There's no such thing as a schemaless system. There are systems where you write your schema down and ones where you don't. There's no such thing as a schemaless database. So we do require you to be explicit about this part of your database.

The issue is not whether a database needs an explicit schema. The issue is whether the language you write down your schema in can express the data model you would like to use.

That said, the Datomic schemas, along with the "datom" model, do look expressive.